I need the 1MHs for the MCP4728 to shorten the loops. I need a large set of DAC, and on the same I2C I would use the MCP23017.
Thanks for suggestions!
I though, anything can work under 1.7MHz (I am not professional in electronics...)
I use it at 3.3V. It is possible to us it at higher voltage than the voltage of the teensy 4.1?
At least test at 400kHz to see if that's the issue... don't think you can use it even at 4.5V, as the minimum Vih is 0.8xVdd so 3.6V. You might find a sweet spot where Vdd is high enough to get 1MHz, and low enough to allow 3.3V (nominal) signals from the Teensy. Or an intermediate bus speed (say 700kHz) which works with 3.3V.
Cheers
Jonathan
By the looks of it the mcp23s17 can have adressing which means that your only need one CS for all the expanders, the other pins are then connected in parallel.
http://www.ermicro.com/blog/?p=1050
Something strange experience: if the pullup is 2.2k ond the sda and 10k on the sca! The 1MHz is working!